The present invention relates to an automatic sewing machine, particularly, to an automatic sewing machine in which a presser device holding the web, such as the cloth to be sewn, is automatically moved in accordance with a predetermined pattern thereby to form a seam (stitched pattern) in a predetermined manner.
In a conventional automatic sewing machine, seam pattern data is read out from pattern data memories under the control of a central processing unit (CPU), the read-out data is applied to a pulse train generating circuit to generate pulses in a number corresponding to the amount of web to be fed in synchronism with the rotation of the sewing machine, and the pulses are applied to a web feed driving mechanism to move a web presser connected to the web feed driving mechanism by a predetermined amount, thereby to form the seam pattern on the web on the basis of the seam pattern data.
According to such an automatic sewing machine, when the CPU detects the termination of a sewing operation, the CPU stops the read-out operation of the seam pattern data from the seam pattern data memory and actuates an oscillation circuit within the pulse train generating circuit to generate a continuous pulse stream, which is applied to the web feed driving mechanism thereby to return the web presser to a predetermined initial position thereof. Therefore, in the conventional control apparatus, the initial position and the end position for sewing are the same, regardless of the seam pattern data. Consequently, such a conventional control apparatus has an advantage that a fault in the sewing pattern can be detected at once, even if the seam pattern is shifted, such as may be due to a malfunction of the pulse motor in the web feed driving mechanism. On the other hand, the conventional control apparatus has a disadvantage that, in the case where there is a shift between the seam pattern and the web as fixed by the web presser frame prior to the start of sewing, it is very difficult to obtain accurate adjustment of the web presser in accordance with the seam pattern. Further, if the actual position is displaced from the desired initial position, time is required for moving the web presser frame to the desired initial position, thereby reducing the production performance.